Dilution-Tolerant Organoboron Catalyst for the Copolymerization of CO ₂ and Propylene Oxide Enabled by a Cyclic Anhydride

Developing dilution-tolerant organoborane catalysts for efficient CO2/propylene oxide (PO) copolymerization remains a key challenge. Herein, we report a cyclic anhydride (CA)-enhanced active species strategy that dramatically improves the performance of Lewis pairs comprising Lewis acid (triethylborane, Et3B) and diverse Lewis bases (LBs) such as triaminophosphines, tertiary amines, and tertiary phosphines. This approach features excellent operational simplicity and broad applicability. The optimized catalytic system enables exceptional dilution tolerance (PO/LB = 10,000:1), delivering a record productivity of 1.1 kg polymer per g catalyst at 80 °C. It also operates efficiently at 100 °C, exhibiting a 24-fold higher activity (turnover frequency = 1159 h–1) with high poly(propylene carbonate) selectivity (84%). Mechanistic insights indicate that CA-derived zwitterions are crucial, where the onium cation activates the epoxide and stabilizes the propagating chain end in cooperation with Et3B, while the carboxylate initiates polymerization. This work provides a general paradigm for designing highly active organoboron catalysts via in situ zwitterion engineering, enabling the scalable production of CO2-based polymers in a green manner.